Display devices such as a liquid crystal panel having passive optical modulation elements is provided with a light source for illuminating the optical modulation elements. Optical modulation elements are responsive to an input image signal to vary the amount of passage of light emitted from the light source, thereby to form an image and display it. When “black” is displayed, the optical modulation elements are in a state of shutting the light emitted from the light source. However, even in the “shutting” state, the light transmittance cannot be made zero, and there is some leakage of light. As a result, even the “black” screen has some brightness (“black offset” due the light leakage).
It has been proposed to control the light source according to the content of the image to be displayed, in order to reduce the black offset. In one method, the light source is controlled evenly throughout the screen. For instance, when the screen is dark, the amount of light from the light source is reduced in order to reduce the black offset. However, a bright image part which may be included in a dark screen is also displayed darkly due to the reduction in the amount of illuminating light, and the dynamic range of the display luminance is reduced.
The below-noted Patent Reference 1 discloses a display device in which the light source of the back light is divided into a plurality of partial regions, and the luminance is controlled region by region, in order to reduce or suppress the black offset, and to enlarge the display luminance dynamic range. In the display device disclosed in Patent Reference 1, the luminance set values for each partial region is renewed using a value obtained by weighting the luminance set value of each partial region, and the luminance set values of adjacent partial regions.